This invention relates to radiation therapy of proliferative disease as required adjuvant care following surgical resection of tumors or other pathological conditions. More particularly, it pertains to the intraoperative application of therapeutic radiation emitted from radiation sources positioned within the resection cavity created by surgical resection. Discussion herein is largely directed to radiotherapy following at least partial resection of breast tumors, but it is to be understood that the apparatus and methods may be applied to different anatomical sites.
It has been demonstrated in many areas of surgical oncology that adjuvant radiation treatment following tumor resection reduces the likelihood of recurrence of cancer or other proliferative disease. The likelihood of infiltrative disease decreases with distance from a primary site in a tissue with confirmed disease. It has also been shown that brachytherapy delivered from within the resection cavity is as effective as external beam therapy, reduces exposure of normal tissue to inadvertent radiation exposure, and furthermore, that quality of life is superior after brachytherapy compared to that following external beam therapy. It is therefore desirable that brachytherapy or brachytherapy-like techniques be made available to as great a population of patients as possible.
Many radiotherapists prefer to deliver radiotherapy in fractions spaced in time (over a period of several days or even weeks) using intracavitary brachytherapy techniques to take advantage of the fact that normal cells recover from radiation exposure in a shorter period of time than diseased cells. Other radiotherapists have found intraoperative radiation therapy (IORT, radiotherapy delivered during the same operative procedure as the tumor resection) to be equally if not more effective in many circumstances, and may offer the opportunity for simultaneous reconstructive surgery. This invention pertains to IORT, or delivery of other single-treatment radiotherapy wherein a complete treatment or prescription is delivered from the resection cavity in one dose during a conventional open surgical procedure. It has also been demonstrated that radiation intensity diminishes with distance from the radiation source. Radiotherapists fairly universally have therefore found that it is generally desirable to spatially separate the radiation source from the tissues being treated. This reduces the likelihood of exposing normal tissue to harmful levels of radiation, particularly that tissue nearest the radiation source, while still delivering the prescribed radiation to the prescribed depth. In a situation where the resection cavity is substantially centered on the site of the tumor, the prescription depth is the depth in tissue outside the resection cavity where the likelihood of undiagnosed disease is highest and where adjuvant radiation treatment is warranted. The target tissue is the tissue to which this prophylactic radiotherapy is directed, generally lying outside the resection cavity, but within the bounds of the prescription depth. Where the cavity (and hence the resected tissue specimen) is eccentric about the tumor location, that portion of the cavity farthest from the tumor may require less radiation prescription depth than tissues near the resected tumor location.
To create this spatial separation in traditional intracavitary brachytherapy, an applicator, usually comprising a balloon, is positioned and inflated within the resection cavity. For the same reasons as above, it is also desirable to create spatial separation preparatory to IORT treatment within an open surgical cavity. At present, however, there are no applicators, analogous to the balloon applicators described above, for use with IORT methods in open surgical fields. A purpose of this invention is to fill that need.
Traditional brachytherapy sources are isotopic seeds, often of iridium 192 positioned on wires, which are manipulated within applicator source guides and balloons to deliver the prescribed treatment to the target tissue surrounding the balloon and resection cavity. Emissions from iridium and other common medical isotopes usually have high-energy components which can penetrate deeply into tissue. They also emit continuously, and thus can only be used in special, heavily-shielded rooms. In addition, concerns for the safety of personnel require isolation of the patient during treatment, shielded storage at all other times, and automated handling between the storage chamber and the applicator when in the patient. In total, the capital expense required for such facilities dictates that treatment centers be located in urban areas so as to serve sizeable patient populations. This can result in under serving rural patients who cannot repeatedly travel to urban treatment centers for a course of prolonged radiation treatment. Furthermore, the need for patient isolation is inconvenient for therapists, not to mention daunting for the patients under treatment. With such brachytherapy, it is clear that any improvements to the total duration of treatment, cost, source handling and shielding difficulties, patient fear factors and inconvenience would be welcome.
Recently, miniature electronic x-ray tubes have provided a preferable alternative to use of isotopes. Such tubes do not emit continuously, they only emit when powered in a manner causing emission and they can be turned on and off, or if desired, modulated such that their penetration depth can be controlled (by control of acceleration voltage) and their dose intensity can be controlled (by filament current) as well. One reference describing the principles and construction of such tubes is Atoms, Radiation and Radiation Protection, Second Edition, John E. Turner, Ph.D., CHP, 1995, John Wiley & Sons, Section 2.10. Electronic brachytherapy sources generally require cooling and are usually contained in a fixed position within a catheter designed for the purpose, but otherwise are more versatile and convenient to use than isotopes, and can be engineered to accommodate a wide variety of dosimetric prescription detail. In addition miniature x-ray tubes can be designed to emit substantially isotropically, or directed to emit only through a predetermined solid angle, permitting more detailed treatment plans. Isotope radiation cannot be controlled in this manner. Furthermore, the x-ray energy spectrum in ranges suitable for brachytherapy or IORT eliminates the need for heavily shielded structures, or “bunkers”, and also permits the therapist to be in the room with the patient during therapy. Therapy can proceed in almost any medical facility, urban, rural or even mobile, and therefore, with miniature x-ray tubes, a greater population of patients can be treated, and the costs of therapy are greatly reduced. It is clear that electronic brachytherapy sources have already contributed significantly to making such therapy more readily available and cost effective than other methods. Treatment duration can still be improved, however, and IORT is a procedure directed to this end.
Tumor resection is usually carried out by open surgical technique where the surgeon proceeds directly through skin and tissue overlying the tumor, or at the surgeon's discretion, from a nearby point which may provide more pleasing cosmesis. The incision must accommodate tumor resection including excision of additional tissue around the tumor, the margins of which are believed to be disease free. Often, efforts are made to provide markers which help orient the tissue with respect to the cavity from which it was excised, and which provide a basis the pathologist and surgeon can use to communicate with respect to the precise location of the tumor within the specimen (thus the cavity) and/or the location of further disease at the margins. Once analyzed, and if necessary, further tissue is removed until the margins are “clear”, or free of apparent disease. In some modern institutions, this pathologic assessment is performed while the patient is still anaesthetized and on the operating table. Once the margins are determined to be free of disease, if IORT is the radiotherapy of choice, it is then administered.
Because the extent of the disease is uncertain at the outset of surgery, the incremental nature of the resection procedure in response to pathological findings may result in a cavity, the boundaries of which are eccentric with respect to tumor, and some margins which are relatively farther removed from the original tumor than others, and thus less likely to be infiltrated with disease. In such a circumstance, the prescription dose can be specified for delivery to an imaginary surface defined in relation the tumor location without reference to the cavity boundaries. It is an object of this invention to accommodate such eccentricity so that tissues lying farthest from the tumor receive a lower dose than those lying near the tumor site, and to facilitate preparation of such a treatment plan.
Other objectives of the invention will become apparent from the following summary, drawings and description.